It is unclear what the firm's role will be for the bank, the report said.

"The GDB regularly solicits advice and counsel from a number of legal and financial advisers with respect to financing plans and other related matters," a spokesman for the GDB said in a statement. "Cleary Gottlieb Steen & Hamilton LLP were engaged by the GDB as part of these ongoing efforts. As is customary, GDB does not comment on the nature or content of any legal advice."

The GDB said in March it hired Millstein & Co. as a financial advisor.

Last month, Puerto Rico sold $3.5 billion in debt, which bought the island another year before it faces immediate restructuring concerns, the report said, citing sources familiar with the matter.

Puerto Rico policymakers pledged to honor debt obligations, which Moody's Investors Service in January estimated would total $18.35 billion through 2018 on both tax-supported bonds and those backed by dedicated revenue flows, Reuters reported last month.